Communication systems are available which provide walkie-talkie-like functionality or similar half-duplex voice functionality which may take the form of PTT™ (Push-To-Talk™) over a dispatch service, PTT™ over cellular (PoC) services (part of the OMA standard), or otherwise. When referred to herein, walkie-talkie-like functionality and half-duplex voice functionality are to be taken generally to mean any voice communication functionality delivered via a network or networks which at any one time is capable of transmitting voice communication from a talking or transmitting party's device to a listening or receiving party's device, but does not simultaneously transmit voice communication from the receiving party's device to the talking party's device, while the talking party's device is transmitting voice to the receiving party's device. It is noted that such devices typically do not exclude other means of data communications, such as Instant Messaging (chat) over wireless, which in fact are defined as part of the OMA specifications to be allowed during a PoC session. During an active PTT™ session or dispatch call session, only one user device (the “talker's” device) participating in the session may be designated as the transmitting or talking device at any one time. A user device gains the role of transmitting device by requesting the talk/transmit channel from the network and by being granted the talk/transmit channel by the network. While a talker's device is in possession of the transmit channel (during a talk period), all of the other devices (listeners' devices) in the active dispatch call session are in listener mode and cannot transmit voice until the transmitting device requests the network to terminate the talk period and release the talk/transmit channel. Times during which the talk/transmit channel is not occupied are idle periods. In standard implementations of PTT™, the user interface of, for example, a wireless device, includes a PTT™ button to allow the user to control the sending of requests to acquire and release the talk/transmit channel, these requests being sent over a logical control channel to the network.
An example of a system providing PTT™ functionality as part of its walkie-talkie-like services is the iDEN™ system of Motorola™. Other example systems which can provide such PTT™ services are 1xRTT CDMA, UMTS, GSM/GPRS, TDMA, and the 802.11 family of standards. Push-to-talk™ service may be provided as an optional half-duplex service over existing network systems which also provide for full duplex communication, or may be provided as a service over network systems which provide only half-duplex communication.
Recent developments have given such mobile stations the ability to communicate in “push-to-talk” (PTT) modes using Push-to-talk over Cellular (PoC) technology as defined by the Open Mobile Alliance (OMA). PoC communication utilizes Voice-over-IP (VoIP) techniques which involve the communication of data packets carrying voice information and use Session Initiation Protocol (SIP) for PoC Session Establishment and RTCP as defined in RFC 3550 for Floor Control Protocol. Floor Control may be known as Talk Burst Control or Media Burst Control.
PoC communication is adapted for one-to-one talks or group talks which are session-based. The end user of a mobile station may send an “invitation” for PoC communication to other potential “participants” who may “accept” or ignore the invitation. When an initiation is accepted, a PoC session is created between the two participants. Further acceptances of the invitation may expand the session into a group session having more than two participants.
One of the problems with using IP based messaging such as RTCP for Talk Burst Control and Media Burst Control particularly in narrow band wireless networks is that IP packets which tend to be relatively large because of IP packet overhead take time to be transmitted between mobile terminal and the network server. This results in delays between one talker speaking and another talker being able to speak.